Embodiments of the present invention relate generally to generators and, more particularly, to high speed generators incorporating positively restrained balance rings.
There is a trend of utilizing more and more electric systems in vehicles such as aircraft. This is due in part to a change over from traditionally non-electric systems, such as hydraulic systems, to electric systems. This trend is also due to the creation of entirely new electric systems that did not exist in the past. Examples include replacing hydraulic actuators with electric motors and the removal of bleed air from cabin pressurization. Consequently, demand for electric power in vehicles continues to increase.
Typically, electric power is generated in a vehicle by one or more electric generators. Due to the increasing power requirements, generators are being run at higher speeds. Such generators may be referred to as “high-speed” generators. Conventional high-speed generators may include, among other elements, a rotor, a shaft, a rotor band at each end of the rotor, coils, coil end turns, interpole wedges, and band supports.
Rotation, such as the rotation of a rotor in a high-speed generator, exerts forces on the elements of the generator. Accordingly, a rotor band is typically placed around the coil end turns. Specifically, band supports are glued or bonded to the coil end turns and the interpole wedges are inserted in between the coils. The rotor band is placed around the band supports and the interpole wedges so as to keep these component parts secure relative to one another and relative to the rotor. As the rotor band, the interpole wedges, and the band supports are all individual pieces, manufacture and maintenance may be complex.
As a revolving part, a rotor may need to be balanced. Conventionally, the rotation of a rotor would be balanced by adding weights at particular locations on a geometric plane referred to as a balance plane. Conceptually, the balance plane may be thought of as extending along x and y axes, while a shaft of a generator may be thought of as extending along the z axis. The rotation of the rotor is around the z axis. By placing weights at particular locations on the balance plane, any rotor unbalance caused during assembly can be reduced to acceptable levels.
In a typical generator, rotor band supports may be used in combination with weights. The band supports are typically shaped pieces of aluminum, flat on the bottom and curved on the outer surface. The balance supports are placed on the top of each end turn and a ring is placed over the balance support/end turn assembly to provide restraint against the radial forces. By placing particular amounts of weight within the band supports, the rotor may be balanced. As noted above, the band supports are individual from one another and from the rotor band and the interpole wedges. Accordingly, the band supports and the interpole wedges may shift or change position relative to one another, even if only so slightly. For example, one band support may shift position relative to another band support as a result of the differing strength of the adhesive bonds created during the epoxy impregnation process. This may not be apparent at the relatively low speeds the rotor is balanced at. At a high rate of speed, such position changes can result in an unbalanced rotor. Further, the band supports do not extend the entire way around the rotor. Weights can only be added to the band supports. Thus, “dead spots” exist where it may be impossible to add balance weights over the complete 360 degrees of the balance plane.
As can be seen, there is a need for a high speed generator improving upon the conventional rotor band, the conventional interpole wedges, the conventional band supports, and the conventional weights. There is also a need for a high speed generator having fewer dead spots on the balance plane. Further, there is a need for a high speed generator that is relatively simple to manufacture and that is relatively simple to maintain once in use.